The present invention relates to a hydrodynamic bearing device for use in an office automation system and an audio-visual system.
Hydrodynamic bearing devices are generally used in rotary head cylinders for tabletop VTRs and camera-incorporated VTRs, in polygon scanner motors for laser copiers, and in recording medium rotation drivers for floppy disk devices and hard disk devices.
Specifically, the hard disk devices have higher memory capacities and higher data transfer speeds. This requires a disk rotating device for use in a recording apparatus of this type to be capable of high-speed and high-precision rotation.
To this end, a hydrodynamic bearing device as disclosed in U.S. Pat. No. 5,504,637 is used for a rotary main shaft of the recording apparatus.
The hydrodynamic bearing device has a construction as shown in FIG. 5.
The hydrodynamic bearing device includes a stationary shaft 1 and a rotary sleeve 2 supported around the stationary shaft 1. The stationary shaft 1 has a proximal end fixed to a lower casing 3. Hard disks 4 are fitted around the rotary sleeve 2.
Dynamic pressure generating grooves 6 are provided in an outer circumferential portion of the stationary shaft 1 in a radial-side dynamic pressure generating portion 5 defined between the stationary shaft 1 and the rotary sleeve 2.
A stationary thrust ring 9 is attached to a distal end of the stationary shaft 1 by an extension shaft 8 formed with a male thread portion 7 threaded with the stationary shaft 1.
The rotary sleeve 2 has a recessed portion 10 provided in association with the stationary thrust ring 9. An opening of the recessed portion 10 is virtually closed by a rotary thrust ring 12 which has at its center a center hole 11 of a diameter greater than the outer diameter of the extension shaft 8. The rotary thrust ring 12 is fixed to the rotary sleeve 2 by a screw 13.
In a thrust-side dynamic pressure generating portion 14 defined by the recessed portion 10 of the rotary sleeve 2, the stationary thrust ring 9 and the rotary thrust ring 12, dynamic pressure generating grooves 15, 16 are provided in upper and lower faces of the stationary thrust ring 9. The thrust-side dynamic pressure generating portion 14 and the radial-side dynamic pressure generating portion 5 are filled with a lubricating fluid.
A stator winding 17 is disposed around a proximal end portion of the stationary shaft 1 on the lower casing 3. A magnet 18 is provided on an inner circumferential surface of the rotary sleeve 2 as opposing to the stator winding 17. The extension shaft 8 is fixed to an upper casing 19 by a screw 20.
In the hydrodynamic bearing device having the aforesaid construction, the hard disks 4 are rotated at a high speed via the rotary sleeve 2 in a sealed space defined between the lower casing 3 and the upper casing 19 upon energization of the stator winding 17.
The rotation of the rotary sleeve 2 about the stationary shaft 1 pumps the lubricating fluid so that the rotary sleeve 2 can maintain non-contact rotation.
However, the aforesaid arrangement has the following drawback.
Due to expansion of the lubricating fluid and a centrifugal force, the lubricating fluid 21 is liable to scatter out of the radial-side dynamic pressure generating portion 5 as indicated by 22 in FIG. 6, or scatter out of a gap between the extension shaft 8 and the rotary thrust ring 12 as indicated by 23, thereby causing lockup or seizure of a motor.
Particularly, where the scattered lubricating fluid adheres onto the hard disks 4, erroneous data reproduction may result.
More specifically, a conventional technical approach to the prevention of the scattering of the lubricating fluid from the open end of the thrust-side dynamic pressure generating portion is to reduce the radial spacing of the gap as much as possible.
Further, improvement in shock resistance with respect to the thrust direction is currently demanded. This demand is directed not only to a hydrodynamic bearing device constructed such that a stationary shaft is fixed at its opposite ends as described above, but also to a hydrodynamic bearing device constructed such that the stationary shaft is fixed only at its proximal end.
It is therefore an object of the present invention to provide a hydrodynamic bearing device which has an improved construction to prevent a lubricating fluid from scattering out of a dynamic pressure generating portion.
The hydrodynamic bearing device of the present invention is characterized in that a radial spacing of a gap at an open end of a thrust-side dynamic pressure generating portion is set greater than a spacing of the thrust-side dynamic pressure generating portion as measured with respect to the thrust direction.
With this arrangement, the scattering of the lubricating fluid from the open end of the thrust-side dynamic pressure generating portion can be prevented even when the hydrodynamic bearing device is operated at a high rotation speed in a high temperature environment.
In accordance with a first aspect of the present invention, there is provided a hydrodynamic bearing device which comprises a stationary shaft having opposite ends at least one of which is fixed and a rotary sleeve supported rotatably about the stationary shaft and is adapted to pump a lubricating fluid between the stationary shaft and the rotary sleeve for non-contact rotation of the device, wherein the stationary shaft is provided with a stationary thrust ring, wherein the rotary sleeve has a recessed portion defined by faces thereof opposed to upper and lower faces and outer circumferential surface of the stationary thrust ring, wherein the lubricating fluid is filled in a gap defined between the stationary thrust ring and the recessed portion, wherein the following expression is satisfied:
xcex94L=t+10 xcexcm to 30 xcexcm [10 xcexcmxe2x89xa6xcex94Lxe2x88x92txe2x89xa630 xcexcm]
wherein t is a thickness of the stationary thrust ring and xcex94L is a height of the recessed portion.
In accordance with a second aspect of the present invention, the hydrodynamic bearing device is characterized in that the stationary shaft is supported at its fixed opposite ends, that a radial-side dynamic pressure generating portion is defined between the stationary shaft and the rotary sleeve and a thrust-side dynamic pressure generating portion is defined between the stationary thrust ring and the recessed portion and disposed on one side of the radial-side dynamic pressure generating portion, that the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with the lubricating fluid, and that a radial spacing xcex94d of a gap at an open end of the thrust-side dynamic pressure generating portion satisfies the following expression:
xcex94d greater than xcex94Lxe2x88x92t
In accordance with a third aspect of the present invention, there is provided a hydrodynamic bearing device which comprises a stationary shaft supported at its fixed opposite ends and a rotary sleeve supported rotatably about the stationary shaft and is adapted to pump a lubricating fluid between the stationary shaft and the rotary sleeve for non-contact rotation of the device, wherein the stationary shaft is provided with a stationary thrust ring, wherein the rotary sleeve has a recessed portion defined by faces thereof opposed to upper and lower faces and outer circumferential surface of the stationary thrust ring, wherein a radial-side dynamic pressure generating portion is defined between the stationary shaft and the rotary sleeve and a thrust-side dynamic pressure generating portion is defined between the stationary thrust ring and the recessed portion and disposed on one side of the radial-side dynamic pressure generating portion, wherein the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with the lubricating fluid, wherein a radial spacing xcex94d of a gap at an open end of the thrust-side dynamic pressure generating portion satisfies the following expression:
xcex94d greater than xcex94Lxe2x88x92t
wherein t is a thickness of the stationary thrust ring and xcex94L is a height of the recessed portion.
In accordance with a fourth aspect of the present invention, the hydrodynamic bearing device comprises: a stationary shaft having a proximal end fixed to a casing; a rotary sleeve supported rotatably about the stationary shaft and having an open portion provided adjacent one end thereof in association with a distal end of the stationary shaft, the opening having a diameter greater than a diameter of the stationary shaft, the rotary sleeve having an outer circumference to which a load member is attached; a stationary thrust ring of a disk shape having a through-hole at its center and attached to the distal end of the stationary shaft, the stationary thrust ring having a lower face opposed to a bottom of the open portion of the rotary sleeve and an outer circumferential surface opposed to an inner circumferential surface of the open portion; an extension shaft having a proximal end threaded with the distal end of the stationary shaft thereby fixing the stationary thrust ring to the stationary shaft; and a rotary thrust ring of a disk shape fitted in the open portion of the rotary sleeve and having at its center a through-hole through which the extension shaft extends, wherein a dynamic pressure generating groove is provided in a radial-side dynamic pressure generating portion defined by an outer circumferential portion of the stationary shaft and an inner circumferential portion of a center hole formed in the rotary sleeve, wherein dynamic pressure generating grooves are provided in a thrust-side dynamic pressure generating portion defined by the stationary thrust ring, the inner circumferential surface of the open portion of the rotary sleeve and faces of the rotary sleeve opposed to the stationary thrust ring, wherein the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with the lubricating fluid, wherein a distal end of the extension shaft is fixed to the casing.
In accordance with a fifth aspect of the present invention, the hydrodynamic bearing device according is characterized in that xcex94d is 10 xcexcm to 30 xcexcm.